Evident but context‐dependent mortality of fish passing hydroelectric turbines

Abstract

Globally, policies aiming for conservation of species, free‐flowing rivers, and promotion of hydroelectricity as renewable energy and as a means to decarbonize energy systems generate trade‐offs between protecting freshwater fauna and development of hydropower. Hydroelectric turbines put fish at risk of severe injury during passage. Therefore, comprehensive, reliable analyses of turbine‐induced fish mortality are pivotal to support an informed debate on the sustainability of hydropower (i.e., how much a society is willing to pay in terms of costs incurred on rivers and their biota). We compiled and examined a comprehensive, global data set of turbine fish‐mortality assessments involving >275,000 individual fish of 75 species to estimate mortality across turbine types and fish species. Average fish mortality from hydroelectric turbines was 22.3% (95% CI 17.5–26.7%) when accounting for common uncertainties related to empirical estimates (e.g., handling‐ or catch‐related effects). Mortality estimates were highly variable among and within different turbine types, study methods, and taxa. Technical configurations of hydroelectric turbines that successfully reduce fish mortality and fish‐protective hydropower operation as a global standard could balance the need for renewable energy with protection of fish biodiversity.

Fish Injury from Movements across Hydraulic Structures: A Review

“…Despite efforts to create safer versions of pumps and turbines, studies have shown that "fish-friendly" does not universally apply to all species [127]. In both cases, strike is assumed as one of the most severe causes of injury and death for fish travelling through these systems, identifying the cause for death is difficult however, as fish may have been injured or died before reaching the blades [23,43,115]. These sites should aim to provide effective bypasses that avoid all turbomachinery.…”

“…Fish often incur severe injuries moving through hydroelectric turbines, with mortality averaging 22.3% around the world [115]. Turbines are usually large, extract energy from water, generating considerable pressure changes just after the turbine, where fish are highly vulnerable to strike by blades, collision and shear (Figure 5c).…”

“…Blades in the turbines are the most dangerous regions [9,85] and most common cause of injury [119,120]. Injuries and death increase with faster rotations and more blades per turbine [32,33,119,[121][122][123][124]; and increased fish length [8,32,33,57,98,115,120]. Mid-body strikes cause more death than tail strikes [72].…”

“…A key difficulty in turbine studies is identifying a definite cause of injury or death [23,43]. Fish may have been injured or died before reaching the turbine [115] with blade strike disguising the initial injuries or cause for mortality. There is a need to systematically investigate other potentially injurious components such as intakes, connections and draft tubes in hydropower systems beyond the actual turbine.…”

Boyle’s Law ignores dynamic processes in governing barotrauma in fish

“…The development of water infrastructure, for purposes such as power generation, water level management and flood defence, is considered one of the greatest threats to the conservation of freshwater ecosystems 2 , posing substantial challenges for sustainable development. For fish that move between critical habitats fragmented by river infrastructure, injury and mortality is common among those that transit via hazardous routes, with one in five (22.3%) that pass through hydropower turbines killed 3 and similar or higher levels frequently reported for pumps 4 , 5 . Barotrauma from exposure to abrupt pressure change is thought to be a key contributing factor to turbine and pump passage mortality 6 , 7 .…”